Rapid proliferation of information communication equipment, especially, small devices for personal use, such as portable terminals, has demanded further enhancement of performance, for example, higher integration, higher speed, and lower power consumption of constituent devices, such as memory devices and logic devices, thereof. Especially, the improvements in high density and high capacity of nonvolatile memories have become important as techniques for replacing hard disks and optical disks, the miniaturization of each of which is inherently impossible due to the presence of moving parts.
Flash memory using a semiconductor, and FRAM (Ferroelectric Random Access Memory) using ferroelectric substance are cited as nonvolatile memories. However, the flash memory has drawbacks in that the high integration of the flash memory is difficult because of complexity in structure thereof, and that an access time is 100 nm or so and thus slow. On the other hand, it is pointed out that FRAM has a drawback in that the possible number of rewritable times is small.
Nonvolatile memory attracting attention as having no such drawbacks is, for instance, a magnetic memory referred to as MRAM (Magnetic Random Access Memory) or MR (Magnetic resistance) memory, which is described in an article by Wang et al., IEEE Trans. Magn. 33 (1997) p448. Because MRAM has a simple structure, high-integration thereof is easily achieved. Further, writing is performed thereon by rotation of a magnetic moment, so that, the possible number of rewriting times is expected to be large. Furthermore, even with regard to the access time that was a problem just after the proposal of MRAM, however, a high output can be obtained by utilization of TMR (Tunnel Magnetic Resistance) effects, so that access time is, nowadays, considerably improved.
However, MRAM has an essential problem in structure. Writing in MRAM is performed by causing a current magnetic field, which is generated by supplying current to wiring, to rotate magnetization of a recording layer. Nevertheless, as the wiring becomes thinner due to the high integration, the critical current value of current that can be supplied to a write line decreases, so that the magnitude of an obtained magnetic field decreases. Thus, the coercive force of a recorded region should be reduced. This means that the reliability of the information writing device lowers. Further, it is considered that because a magnetic field cannot be converged different from light and electron beams, the magnetic field is a principal cause of a crosstalk in the case of achieving the high integration. Although a keeper structure has been proposed so as to prevent an occurrence of this situation, the complication of the structure of MRAM is unavoidable. As above-described, writing utilizing the current magnetic field essentially has many problems and may cause major drawbacks of MRAM in future.
Meanwhile, such drawbacks can be solved in the case that magnetization can be controlled without using a magnetic field. Further, a technique of stacking and using ferromagnetic/semiconductor/ferromagnetic layers as means for controlling magnetization without using a magnetic field, as described by Mattson et al., Phys. Rev. Lett. 77 (1993) p. 185.
This utilizes the fact that magnetic coupling between ferromagnetics depends upon the carrier concentration of the semiconductor layer serving as an intermediate layer. In a multilayered element obtained by stacking the ferromagnetic/semiconductor/ferromagnetic layers, the magnetic coupling between the ferromagnetic layers can be changed, for example, from a parallel one to an antiparallel one by controlling the carrier concentration of the semiconductor layer serving as an intermediate layer. Thus, when the magnitude of the coercive force of one (that is, a fixed layer) of the ferromagnetic layers is set to be large, the magnetization of the other ferromagnetic layer (that is, a movable layer) can be turned with respect to the fixed layer. Especially, a method of turning the magnetization by utilizing an electrical input is promising as a technique for realizing a compact all-solid-state device.
Various structures of such information writing devices are reported. To cite one example, there is a structure in which various kinds of films including magnetic films serving as constituent elements of the information writing devices are stacked in such a way as to be parallel to bit lines and word lines, as disclosed in Japanese Patent Application Laid-Open No. Hei 11-317071. Method of manufacturing such a structure is to form various kinds of films including magnetic films, which serve as constituent elements of the information writing device, and to thereafter shape the films into a predetermined form, such as a rectangle, by utilizing a photolithography technique and a dry-etching technique.
However, it is becoming difficult to finely work such structures, which includes a multi-layered film necessary to be finely processed in manufacturing a multilayered element obtained by stacking ferromagnetic/semiconductor/ferromagnetic layers, with high precision. Furthermore, with the fine processing of the multilayered film, the required area of the information writing device cannot be secured. This results in increase in the resistivity of the device and the power consumption thereof and also results in degradation of the reliability thereof. Problems of the invention are to solve the difficulties of a method of manufacturing the above-mentioned conventional structure, and to manufacture information writing devices at low cost with high precision.